JPH09316223A - Foam plate comprising modified polypropylene resin composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a foam plate of polypropylene resin composition with high strength and good appearance. SOLUTION: This foam plate is obtained by kneading a foaming agent into a modified polypropylene resin composition prepared by reaction of a polypropylene resin, an aromatic vinyl monomer and a radical polymerization initiator, then extruding the kneaded product. This foamed product has an apparent density of 10-300kg/m<3> , a thickness of >=10mm, the average diameter of foams measured in the transverse direction (LTD), in the extruding direction (LMD) and in the thickness direction (LVD) are in the range from 0.1 to 3mm, respectively, where both of RMD/ TD and RVD/ TD are in the range of 0.3 to 3 when the ratio of LMD to LTD is defined as RMD/ TD and that of LVD to LTD, as RVD/ TD.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plate-like foam comprising a polypropylene-based resin, an aromatic vinyl monomer, and a modified polypropylene-based resin composition obtained by a reaction with a radical polymerization initiator.

[0002]

2. Description of the Related Art A foam made of a thermoplastic resin is generally used for a heat insulating material, a cushioning material, a core material, a food container, etc. because it is lightweight and has a good heat insulating property and a good shock absorbing property against external stress. ing.

[0003] Foams using a polyolefin-based resin as a base resin are mainly used for low-density polyethylene, but polyethylene-based resins have a drawback that heat resistance is extremely poor. On the other hand, polypropylene-based resins have high elasticity, and are excellent in solvent resistance, heat resistance, hinge characteristics, and the like, so that an extremely wide range of use as a foam can be expected. However, the viscosity and tension at the time of melting are low,
Therefore, the strength of the cell wall was not sufficiently maintained during foaming, and it was difficult to form a thick foam such as a polyethylene resin.

In recent years, a method for producing a foam using polypropylene having a long-chain branched structure has been reported (Japanese Patent Laid-Open No. 5-506875 and the like). However, this method uses a special resin. Since it lacks versatility and the raw material resin is expensive, it cannot be said to be an industrially useful method. Further, this method can only produce a thin foam having a wall thickness of 10 mm or less.

[0005]

The present invention is obtained by foaming a modified polypropylene resin composition obtained by the reaction of a polypropylene resin, an aromatic vinyl monomer, and a radical polymerization initiator, and has a strength of The object is to provide a plate-like foam which is high and has a beautiful appearance.

[0006]

Means for Solving the Problems The present inventors have made detailed studies on a plate-like foam made of a modified polypropylene resin composition modified by a specific method, and as a result, have found that the foam has a density and a bubble content. It was found that the size and the shape of cells and the strength of the plate-shaped foam are closely related to each other, and the present invention has been completed.

The present invention relates to a polypropylene resin (hereinafter,
A polypropylene resin before modification is referred to as "raw polypropylene resin"), a modified polypropylene resin composition obtained by reacting an aromatic vinyl monomer and a radical polymerization initiator with a foaming agent. Then, the modified polypropylene resin composition in which a foaming agent is kneaded is extruded to obtain an apparent density of the foam of 10
In the range of ~300kg / m ^3, is not less 10mm or more thick, the average diameter L _TD bubble measured along the width direction of the foam, bubble measured along the extrusion direction of the foam The average diameter L _MD and the average diameter L _{VD of the} bubbles measured along the thickness direction of the foam are both within the range of 0.1 to 3 mm, and the average diameter L of the bubbles with respect to the average diameter L _TD of the bubbles.
_When the ratio of _MD is R _{MD / TD} and the ratio of the average diameter L _VD of bubbles to the average diameter L _TD of bubbles is R _{VD / TD} , both R _{MD / TD} and R _{VD / TD} are 0.3. The present invention relates to a plate-like foam made of a modified polypropylene resin composition within the range of 3 to 3.

The present invention also relates to a plate-like foam made of the modified polypropylene resin composition having a closed cell ratio of 60% or more.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The plate-like foam of the present invention is characterized by comprising a specific modified polypropylene resin composition and having a specific density, average cell diameter and cell shape.

The above specific modified polypropylene resin composition can be obtained by reacting a raw material polypropylene resin, an aromatic vinyl monomer and a radical polymerization initiator.

The modified polypropylene resin composition thus obtained has improved foamability. It is not clear why the modified polypropylene resin composition has improved foamability, but which of the raw material polypropylene resin, the aromatic vinyl monomer, and the radical polymerization initiator is missing. Even in such a case, a modified polypropylene resin composition having desired properties cannot be obtained.

Examples of the starting polypropylene resin usable in the present invention include propylene homopolymer, block copolymer of propylene and other monomers or random copolymer of propylene and other monomers. A propylene homopolymer is preferred in terms of high rigidity and low cost, and a block copolymer of propylene and another monomer is preferred in terms of both high rigidity and high impact resistance. Polymers are preferred. When the raw polypropylene resin is a block copolymer of propylene and other monomers or a random copolymer of propylene and other monomers, high crystallinity, which is characteristic of the raw polypropylene resin, is high. From the viewpoint of maintaining rigidity and good chemical resistance, the content of the propylene monomer component is preferably at least 75% by weight, more preferably at least 90% by weight.

In the raw material polypropylene resin,
As other monomers copolymerizable with propylene, one or more selected from the group consisting of ethylene, α-olefin, cyclic olefin, diene monomer and vinyl monomer Monomers. Further, as the monomer, ethylene, α-olefin or diene-based monomer is preferable because it is easily copolymerized with propylene and is inexpensive.

Examples of the above-mentioned α-olefin copolymerizable with propylene include butene-1, isobutene, pentene-1,3-methyl-butene-1, hexene-1,3-.
Methyl-pentene-1, 4-methyl-pentene-1,
Α-olefins having 4 to 12 carbon atoms, such as 3,4-dimethyl-butene-1, heptene-1, 3-methyl-hexene-1, octene-1, and decene-1. Examples of the cyclic olefin copolymerizable with propylene include cyclopentene, norbornene, 1,4.
5,8-Dimethano-1,2,3,4,4a, 8,8a-
6-octahydronaphthalene and the like. Also,
Examples of the diene-based monomer copolymerizable with propylene include 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7- Methyl-1,6-octadiene and the like can be mentioned. Further, examples of the vinyl monomer copolymerizable with the above-mentioned propylene include vinyl chloride,
Examples thereof include vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, ethyl acrylate, butyl acrylate, methyl methacrylate, maleic anhydride and the like.

Of these monomers, ethylene or butene-1 is more preferable because it is inexpensive.

The molecular weight (weight average molecular weight) of the raw material polypropylene resin is preferably in the range of 50,000 to 2,000,000 from the viewpoint of easy availability, and from 100,000 to 1,000,000 from the viewpoint of low cost. More preferably, it is within the range.

If necessary, other resin or rubber may be added to the raw material polypropylene resin within a range not impairing the effects of the present invention.

Further, if necessary, the above-mentioned raw material polypropylene resin may be an antioxidant, a metal deactivator, a phosphorus processing stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, an optical brightener,
Stabilizers or crosslinkers such as metal soaps, antacid adsorbents, chain transfer agents, nucleating agents, lubricants, plasticizers, fillers, reinforcing materials, pigments,
Additives such as dyes, flame retardants, and antistatic agents may be added as long as the effects of the present invention are not impaired.

These starting polypropylene resins (which may contain various kneading materials) may be in the form of particles or pellets, and their size and shape are not particularly limited. Absent.

Further, the kneading material (other resin, rubber,
When a stabilizer and / or an additive) is used, even if this kneading material is added to the raw material polypropylene resin in advance, this raw material polypropylene resin is used to start the aromatic vinyl monomer and radical polymerization initiation. It may be added at the time of reacting with the agent. Further, the modified polypropylene resin composition may be added to the modified polypropylene resin composition by an appropriate method after producing the modified polypropylene resin composition.

Examples of the aromatic vinyl monomer that can be used in the present invention include styrene; o-methylstyrene and m.
-Methylstyrene such as methylstyrene, p-methylstyrene, α-methylstyrene, β-methylstyrene, dimethylstyrene and trimethylstyrene; α-chlorostyrene, β-chlorostyrene, o-chlorostyrene, m-
Chlorostyrene such as chlorostyrene, p-chlorostyrene, dichlorostyrene and trichlorostyrene; bromostyrene such as o-bromostyrene, m-bromostyrene, p-bromostyrene, dibromostyrene and tribromostyrene; o-fluorostyrene, m -Fluorostyrene such as fluorostyrene, p-fluorostyrene, difluorostyrene and trifluorostyrene; nitrostyrene such as o-nitrostyrene, m-nitrostyrene, p-nitrostyrene, dinitrostyrene and trinitrostyrene; o-hydroxystyrene , Vinylphenol such as m-hydroxystyrene, p-hydroxystyrene, dihydroxystyrene and trihydroxystyrene; o-divinylbenzene, m-divinylbenzene, p
-Divinylbenzene such as divinylbenzene; one or more kinds of isopropenylstyrene such as o-diisopropenylbenzene, m-diisopropenylbenzene and p-diisopropenylbenzene. Of these, styrene or methylstyrene is preferred because the closed cell ratio and expansion ratio of the foam of the present invention can be particularly increased.

The amount of the aromatic vinyl monomer used is 100 parts by weight of the raw polypropylene resin.
0.1 to 100 parts by weight, particularly 0.1 to 50 parts by weight, sufficiently improves the foamability of the raw material polypropylene-based resin, and has suitable heat resistance and chemical resistance of the raw material polypropylene-based resin. It is preferable in that characteristics such as mechanical characteristics are not impaired.

Examples of the radical polymerization initiator include peroxides and azo compounds. In the present invention, a radical polymerization initiator having a hydrogen abstraction ability with respect to the polymer molecules of the raw material polypropylene resin is used. The presence of compound is required.

Examples of the radical polymerization initiator include peroxides and azo compounds, and specifically, ketone peroxides such as methyl ethyl ketone peroxide and methyl acetoacetate peroxide;
1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, n-butyl-4,4-bis (t-butylperoxy) Peroxy ketals such as valerate, 2,2-bis (t-butylperoxy) butane; permethane hydroperoxide, 1,1,
3,3-tetramethylbutyl hydroperoxide,
Hydroperoxides such as diisopropylbenzene hydroperoxide and cumene hydroperoxide; dicumyl peroxide, 2,5-dimethyl-2,
5-di (t-butylperoxy) hexane, α, α′-
Bis (t-butylperoxy-m-isopropyl) benzene, t-butylcumyl peroxide, di-t-butylperoxide, 2,5-dimethyl-2,5-di (t
-Butylperoxy) hexyne-3 and other dialkyl peroxides; benzoyl peroxide and other diacyl peroxides; di (3-methyl-3-methoxybutyl) peroxydicarbonate, di-2-methoxybutylperoxydicarbonate, etc. Peroxydicarbonate; t-butylperoxyoctate, t-butylperoxyisobutyrate, t-butylperoxylaurate, t-butylperoxy-3,5,5-trimethylhexanoate, t- Butyl peroxyisopropyl carbonate, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-butyl peroxyacetate, t-butyl peroxybenzoate, di-t-
One or more organic peroxides such as peroxyesters such as butylperoxyisophthalate may be used. Among these, those having a particularly high hydrogen abstraction ability are preferable, and as such a radical polymerization initiator,
For example, 1,1-bis (t-butylperoxy) -3,
3,5-trimethylcyclohexane, 1,1-bis (t
-Butylperoxy) cyclohexane, n-butyl-
4,4-bis (t-butylperoxy) valerate,
Peroxyketals such as 2,2-bis (t-butylperoxy) butane; dicumyl peroxide, 2,5-
Dimethyl-2,5-di (t-butylperoxy) hexane, α, α′-bis (t-butylperoxy-m-isopropyl) benzene, t-butylcumyl peroxide, di-t-butylperoxide, Dialkyl peroxides such as 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3; diacyl peroxides such as benzoyl peroxide; t-butylperoxyoctate, t-butylperoxyiso Butyrate, t-butylperoxylaurate, t-butylperoxy-3,5,5-trimethylhexanoate, t-
Butyl peroxyisopropyl carbonate, 2,5-
One or two of peroxyesters such as dimethyl-2,5-di (benzoylperoxy) hexane, t-butylperoxyacetate, t-butylperoxybenzoate, and di-t-butylperoxyisophthalate, or 2
There are more than one seed.

The amount of the radical polymerization initiator used is 100% by weight of the raw material polypropylene resin, from the viewpoint that the melt viscosity of the modified polypropylene resin composition does not excessively decrease and it is economical. It is preferably in the range of 0.01 to 10 parts by weight, and more preferably in the range of 0.5 to 5 parts by weight.

When the amount of the radical polymerization initiator used is less than the above range, the modifying effect tends not to be sufficiently obtained, while when it is more than the above range, it has a suitable shape and appearance. Foams tend not to be obtained.

The modified polypropylene resin composition of the present invention comprises a raw material polypropylene resin, an aromatic vinyl monomer, a radical polymerization initiator, and, if necessary, other copolymerizable copolymers with the aromatic vinyl monomer. It may be produced by reacting with a vinyl monomer.

In the present invention, the method for producing the modified polypropylene resin composition from the raw material polypropylene resin, the aromatic vinyl monomer and the radical polymerization initiator is not particularly limited, and the impregnation polymerization method, the melt kneading polymerization method, etc. Although a generally used method can be adopted, the melt-kneading polymerization method is particularly preferably used because the modified polypropylene resin composition can be continuously produced.

The method of mixing the raw material polypropylene resin, the aromatic vinyl monomer, the radical polymerization initiator and other kneading materials added as necessary is not particularly limited. -Based resin, aromatic vinyl monomer, radical polymerization initiator, and other kneading materials that are added as necessary may be mixed and then reacted (melt kneaded), or the raw polypropylene resin is melted. After kneading, an aromatic vinyl monomer, a radical polymerization initiator, and other kneading materials added as necessary may be simultaneously or separately, mixed together or separately and reacted. (It may be melt-kneaded).

The heating temperature at the time of melt kneading is 130 to 4
The temperature of 00 ° C. is preferred in that the raw material polypropylene resin is sufficiently melted and hardly thermally decomposed. The time for melt-kneading is usually 1 to 60 minutes.

The melt kneading device is a roll,
Kneader, Banbury mixer, Brabender, Single-screw extruder, Twin-screw extruder, etc.
Examples of such devices include a horizontal stirrer such as a multi-shaft disk device or a vertical stirrer such as a double helical ribbon stirrer, which can heat a polymer material to an appropriate temperature and knead it while applying an appropriate shear stress. Of these, especially uniaxial or 2
The axial extruder is preferable from the viewpoint of productivity. The melt-kneading may be repeated a plurality of times in order to mix the respective materials sufficiently uniformly.

As described above, the modified polypropylene resin composition of the present invention can be manufactured.

By foaming the modified polypropylene resin composition thus obtained, the desired plate-like foam can be obtained.

As an example of the method for foaming the modified polypropylene resin composition, (1) the modified polypropylene resin composition and the foaming agent are melt-kneaded in a melt extruder and then extruded by a melt extruder. Examples include a method for obtaining a plate-shaped foam, and (2) a method for obtaining a plate-shaped foam by extruding with a melt extruder after adding or press-fitting a foaming agent to a modified polypropylene resin composition in a molten state. However, it is not limited to these methods.

In the case of the above method (1), examples of the foaming agent include a thermal decomposition type foaming agent. Among them, a preferable thermal decomposition type foaming agent is, for example, N, N'-dinitrosopentamethylenetetramine, N, N'-dimethyl-
Nitroso-based foaming agents such as N, N'-dinitrosoterephthalamide; azo-based foaming agents such as azodicarbonamide and barium azodicarboxylate; sulfo such as p, p'-oxybisbenzenesulfonyl hydrazide and p-toluenesulfonyl semicarbazide Hydrazide type foaming agents; one or more kinds of trihydrazinotriazine and the like.

The amount of the above-mentioned foaming agent used (kneading amount) may be selected depending on the type of the foaming agent and the target expansion ratio, but with respect to 100 parts by weight of the modified polypropylene resin composition,
It is preferably in the range of 0.5 to 100 parts by weight.

If necessary, a foam nucleating agent such as sodium bicarbonate-citric acid or talc may be used in combination in order to control the bubble diameter of the plate-like foam to an appropriate size. The foaming nucleating agent used as necessary is usually based on 100 parts by weight of the modified polypropylene resin composition.
It is used by adding 0.01 to 1 part by weight.

In the case of the above method (1), for example, the modified polypropylene resin composition and the pyrolytic foaming agent are both supplied to a melt extruder, and foamed while being melt-kneaded at an appropriate temperature. A gas is generated by thermally decomposing the agent, and a modified polypropylene resin composition in a molten state containing the gas is discharged from a die, whereby a plate-shaped foam can be formed. The melt-kneading temperature and the melt-kneading time in this method may be appropriately selected depending on the foaming agent and the kneading conditions to be used, and vary depending on the type of the resin. Is usually

In the case of the above method (2), examples of the foaming agent include volatile foaming agents. Among them, preferable volatile foaming agents include, for example, propane, butane, pentane, hexane and heptane. Hydrocarbons; alicyclic hydrocarbons such as cyclobutane, cyclopentane, cyclohexane; chlorodifluoromethane, difluoromethane, trifluoromethane, trichlorofluoromethane, dichloromethane, dichlorofluoromethane, dichlorodifluoromethane, trichlorofluoromethane, chloromethane, Chloroethane, dichlorotrifluoroethane, dichlorofluoroethane, chlorodifluoroethane, dichloropentafluoroethane, tetrafluoroethane, difluoroethane, pentafluoroethane, trifluoroethane, diqua Halohydrocarbons such as rotetrafluoroethane, trichlorotrifluoroethane, tetrachlorodifluoroethane, chloropentafluoroethane, perfluorocyclobutane; inorganic gases such as carbon dioxide, nitrogen, air; one or two kinds such as water The above is mentioned.

The amount of the above-mentioned foaming agent used (kneading amount) varies depending on the type of the foaming agent and the target expansion ratio, but is 0.5 to 100 parts by weight of the modified polypropylene resin composition.
It is preferably in the range of 100 parts by weight.

Also in this method, a foam nucleating agent such as sodium bicarbonate-citric acid or talc may be used together, if necessary, in order to control the cell diameter of the plate-like foam to an appropriate size. . The amount of the foam nucleating agent used, if necessary, is usually preferably 0.01 to 1 part by weight based on 100 parts by weight of the modified polypropylene resin composition.

In the case of the above method (2), for example, the modified polypropylene resin composition is melted in an extruder, and the volatile foaming agent is pressed into the extruder and melted while being kept at a high pressure. Kneaded with the modified polypropylene resin composition in the state, and a kneaded body of the fully kneaded modified polypropylene resin composition and the volatile foaming agent is discharged from a die to form a plate-like foam. sell. The melt-kneading temperature and the melt-kneading time in this method may be appropriately selected depending on the plate-like foaming agent used and the kneading conditions,
The melt-kneading temperature is 130 to 3 depending on the type of resin.
It is usual that the melt kneading time is 1 to 120 minutes at 00 ° C.

The plate-like foam of the present invention has an apparent density of 1
Within the range of 0 to 300 kg / m ³ , preferably 15 to 20
Within the range of 0 kg / m ³ . Apparent density is 10 kg / m ³
When it is less than the above range, the strength of the obtained plate-like foam is lowered.
Such a plate-like foam is particularly difficult to apply as a cushioning material or the like. On the other hand, the apparent density is 300 kg / m
^When it exceeds ³ , it becomes impractical in terms of lightness and price.

The plate-like foam of the present invention must have a thickness of 10 mm or more. If the thickness is less than 10 mm, the impact resistance becomes insufficient. There is no upper limit to the thickness of the plate-like foam of the present invention.

The plate-shaped foam of the present invention has an average cell diameter L _TD measured along its width direction, an average cell diameter L _MD measured along its extrusion direction and its thickness direction. The average diameter L _{VD of the} bubbles measured by
Within the range of m, preferably in the range of 0.2 to 2.5 mm. When at least one of the cell diameters measured along each of the above directions is less than 0.1 mm, the strength of the plate-like foam, particularly the compressive strength, becomes low, while when it exceeds 3 mm, the plate-like foam is obtained. The appearance and feel of the product becomes poor. A plate-like foam body in which at least one of the cell diameters measured along the respective directions does not fall within the above range is particularly difficult to apply as a cushioning packaging material or the like.

The plate-like foam of the present invention is produced by extrusion molding, but the bubbles of the plate-like foam need to have the following shapes. That is, the average diameter of bubbles measured along the extruding direction of the plate-like foam is L _MD , the average diameter of bubbles measured along the width direction is L _TD, and the average diameter of bubbles measured along the thickness direction is The average diameter is L _VD, and the ratio of the average diameter L _MD of the bubbles measured along the extrusion direction to the average diameter L _TD of the bubbles measured along the width direction is R _{MD / TD} .
The ratio of the average diameter L _VD of the bubbles measured along the thickness direction to the average diameter L _TD of the bubbles measured along the width direction is R _{VD / TD}
Therefore, both R _{MD / TD} and R _{VD / TD} are 0.3.
Must be within the range of .about.3, and in each case 0.4 to 2.
It is preferably within the range of 5. The plate-like foam in which at least one of R _{MD / TD} and R _{VD / TD} is not within the above range has a flat shape. Such a plate-like foam having flat cells is not preferable because it has a high cushioning property only against a stress in a flat direction (direction with a short diameter). Further, when the flattening further progresses, the bubbles may break, and the closed cell rate may decrease.

Here, when calculating the cell diameters (L _MD , L _VD , L _TD ) and the cell diameter ratios (R _{MD / TD} , R _{VD / TD} ), they are calculated from specific cut surfaces of the foam. There is a need. Usually, an extruded foam of a thermoplastic resin has a non-foamed or low-foamed thin skin so-called skin layer on the surface, and it becomes necessary to observe bubbles in the portion where the skin layer is removed. . In the plate-shaped foam made of the modified polypropylene resin composition of the present invention, it is necessary to measure the internal cell diameter excluding the skin layer of the plate-shaped foam,
At least 2 mm or more, preferably 4 from the surface layer of the foam
It suffices to measure a portion that is not affected by the skin layer on the inside of mm or more.

Further, the plate-like foam of the present invention has a suitable heat resistance, a better buffering force against external force, and a more suitable compressive strength, so that the closed cell ratio thereof is 60% or more. Is preferred.

Further, the plate-like foam according to the present invention can be particularly suitably used, for example, as a cushioning material as described above.

[0050]

EXAMPLES Next, the present invention will be explained in detail based on examples, but the present invention is not limited to such examples.

Example 1 100 parts by weight of propylene homopolymer (Sumitomo Chemical Co., Ltd., Nobrene D501, melt flow index 0.4 g / 10 minutes at 230 ° C.) and styrene monomer 1
0 parts by weight (manufactured by Wako Pure Chemical Industries, Ltd. (special grade)) and α, α'-bis (t-butylperoxy-m-isopropyl) benzene as a radical polymerization initiator (NOF Corporation)
Manufactured by Japan Steel Works, Ltd., twin-screw extruder (LABOT).
EX) was melt-kneaded and melt-extruded to obtain a rod-shaped modified polypropylene resin composition having a diameter of 4 mm. The molded product of the rod-shaped modified polypropylene resin composition was chopped to a thickness of 3 mm to obtain pellets of the modified polypropylene resin composition.

The twin-screw extruder was of the same-direction twin-screw type, and had a cylinder hole diameter of 32 mmφ and a maximum effective screw length (L / D) of 25.5. The twin-screw extruder was heated at a set temperature of the cylinder section of 200 ° C. and at a set temperature of the feed section of 160 ° C., and the rotation speed of the screw was set to 100 rpm for each axis.

Using the pellets of the modified polypropylene resin composition, a plate-like foam was prepared by the following method.

100 parts by weight of modified polypropylene resin composition pellets, blended oil (Koshigaya Chemical Co., Ltd.)
Made by Super Ease) 0.05 part by weight, and baking soda-citric acid as a foam nucleating agent (manufactured by Eiwa Kasei Co., Ltd., Cerbon S)
G / IC) 0.1 part by weight using a ribbon blender 1
Mix for 5 minutes. This mixture is mixed with a tandem extruder (first
It is fed to a single-stage extruder with a cylinder diameter of 40 mmφ and a second-stage extruder cylinder diameter of 50 mmφ, and melts at 230 ° C. in the first-stage extruder, and then as a foaming agent, butane gas (isorich butane gas; normal butane / isobutane gas). (Mixing ratio 15/85 by weight) is kneaded by injecting 10 parts by weight with respect to 100 parts by weight of the modified polypropylene resin composition, and the mixture is kneaded in the second stage extruder at a temperature of 150 ° C. Cooled to 60 mm width, 0.6 thickness
A plate-like foam was obtained by extruding from a rectangular die having a slit of mm and passing through a molding die directly connected to the rectangular die.

The apparent density, closed cell ratio, average cell diameter, thickness of the obtained plate-shaped foam, and the average diameter of cells measured along the extrusion direction of the plate-shaped foam (hereinafter referred to as "L _MD "). The average diameter of the cells measured along the width direction of the plate-shaped foam (hereinafter also referred to as “L _TD ”), the average of the cells measured along the thickness direction of the plate-shaped foam. Diameter (hereinafter,
“L _VD ”, ratio of L _{MD to} L _TD (hereinafter also referred to as “R _{MD / TD} ”), ratio of L _{VD to} L _TD (hereinafter referred to as “R _{VD / TD} ”. Strength and average bubble diameter were measured by the following methods, and the appearance was visually evaluated by the following evaluation criteria.

Apparent density: Calculated from the weight and the volume obtained by the submersion method.

Independent bubble ratio: Using a multi-pycnometer (product name, manufactured by Yuasa Ionics Co., Ltd.), ASTM D
Measure according to -2856.

Thickness: Measured with calipers.

L _MD : The plate-like foam is placed on a flat surface and cut with a cutter in parallel with the installation plane so that the thickness becomes ½. Scanning electron microscope (SEM)
100 and arbitrarily selected along the extrusion direction.
The diameter of each cell (however, a cell that is at least 2 mm or more inside the tip end in the extrusion direction of the plate-like foam and is present at least 2 mm or more inside the side surface of the plate-like foam) was measured, and its diameter was measured. Calculate the average value and use it as the value of L _MD .

L _TD : The same cross section as in the measurement of L _MD was observed by a scanning electron microscope (SEM), and 100 cells arbitrarily selected along the width direction of the plate-like foam (however, the plate-like foam Bubbles that are at least 2 mm or more inside of the extruding direction of the body and are at least 2 mm or more inside of the side surface of the plate-like foam are measured, and the average value is calculated to calculate L _TD . The value.

L _VD : A plate-like foam is placed on a flat surface and cut along a thickness direction with a cutter so that the volume becomes 1/2. Scanning electron microscope (SE
Observed by M) and arbitrarily selected along the thickness direction 1
The diameter of 00 cells (however, the cells that are at least 2 mm or more inside the extruding direction tip of the plate-shaped foam and are present at least 2 mm or more inside the side surface of the plate-shaped foam are selected), The average value is calculated and used as the value of L _VD .

R _{MD / TD} and R _{VD / TD} : Calculated by the following formulas: R _{MD / TD} = L _MD / L _TD and R _{VD / TD} = L _VD / L _TD .

The value of R _{MD / TD} or R _{VD / TD} is 0.3.
When it is less than 3 or more than 3, the anisotropy of the cushioning property of the external stress becomes remarkable, so that when such a plate-like foam is applied as a cushioning material, a particular inconvenience occurs.

Evaluation of strength anisotropy: The obtained plate-shaped foam was subjected to a compression test in accordance with JIS K 7220 in the extrusion direction, thickness direction and width direction of the foam,
The compressive strength in the extrusion direction, the compressive strength in the thickness direction and the compressive strength in the width direction are measured. A foam having a maximum value of 3 times or less of the minimum value of the respective compressive strengths is evaluated as ○, and a foam having a value of more than 3 times is evaluated as x. The plate-shaped foam having an evaluation result of x has a remarkable anisotropy in strength, and is therefore unsuitable as a cushioning material, for example.

Evaluation Criteria for Surface Condition: ◯: Uniform bubbles, and beautiful appearance. X: Coarse cells are locally generated, foaming is non-uniform, and appearance is not suitable.

As a result, the apparent density was 15 kg / m ³ , the closed cell ratio was 82%, the thickness was 36 mm, L _MD was 2.0 mm, and L _TD was 1.8 mm. , L _VD is 2.3 mm, R _{MD / TD} is 1.1, R _{VD / TD} is 1.3, the strength anisotropy is evaluated as ○, and the surface state is evaluated as ○. there were.

Examples 2 to 3 and Comparative Example 1 In addition to the raw polypropylene resin, aromatic vinyl monomer, and radical polymerization initiator supplied to the twin-screw extruder, the types and amounts thereof were as shown in Table 1. In the same manner as in Example 1, pellets of the modified polypropylene resin composition were obtained.

Using the pellets of the modified polypropylene resin composition, a plate-like foam was obtained in the same manner as in Example 1.

The apparent density, closed cell ratio, average cell diameter, thickness, L _MD , L _TD , L _VD , R _{MD / TD of} this round rod-shaped foam,
R _{VD / TD} , strength anisotropy and surface condition were evaluated in the same manner as in Example 1. The results are shown in Table 2.

Example 4 In Example 1, pellets of the modified polypropylene resin composition were obtained using a twin-screw extruder, and then the pellets were supplied to a tandem type extruder together with a foaming agent and extruded to form a plate-like foam. In this example, the modified polypropylene resin composition was prepared by melt-kneading the raw material propylene resin, the aromatic vinyl monomer and the radical polymerization initiator in the first stage extruder of the tandem type extruder. After further mixing the modified polypropylene resin composition with a foaming agent, the mixture was fed into a second stage extruder, cooled to a predetermined temperature and extruded to obtain a plate-shaped foam.

That is, propylene homopolymer (Sumitomo Chemical Co., Ltd., Nobrene D501, 100 parts by weight and styrene monomer 8 parts by weight (Wako Pure Chemical Industries, Ltd.),
(Special grade)) and 0.6 part by weight of α, α'-bis (t-butylperoxy-m-isopropyl) benzene (Perbutyl P, manufactured by NOF CORPORATION) as a radical polymerization initiator and blended oil (Koshigaya Chemical) Industry Co., Ltd., Super Ease) 0.05 part by weight and sodium bicarbonate as a foam nucleating agent
Citric acid (Cerbon SG / IC manufactured by Eiwa Chemical Co., Ltd.)
0.1 part by weight was mixed for 15 minutes using a ribbon blender. This mixture was supplied to a tandem extruder (the first-stage extruder cylinder diameter was 40 mmφ, the second-stage extruder cylinder diameter was 50 mmφ), and the mixture was heated at 230 ° C. in the first-stage extruder.
Butane gas (iso-rich butane gas; normal butane / isobutane mixing ratio 15/85 by weight) as a foaming agent after being melted in
11 parts by weight of 0 parts by weight was kneaded and kneaded, and the mixture was cooled in the second stage extruder to a resin temperature of 150 ° C., and a rectangular die having a slit having a width of 60 mm and a thickness of 0.6 mm was used. A plate-like foam was obtained by extrusion and passing through a molding die directly connected to a rectangular die.

Apparent density, closed cell ratio, average cell diameter, thickness, L _MD , L _TD , L _VD , R _{MD / TD of} the obtained plate-like foam,
R _{VD / TD} , strength anisotropy and surface condition were measured by the same method as in Example 1. The results are shown in Table 2.

[0073]

[Table 1]

[0074]

[Table 2]

[0075]

The apparent density obtained by foaming a modified polypropylene resin composition obtained by melt-kneading a raw material polypropylene resin, an aromatic vinyl monomer and a radical polymerization initiator is 10 to 20. Is in the range of 300 kg / m ³ , the thickness is 10 mm or more, and the average diameters of the bubbles L _TD , L _MD and L _VD are in the range of 0.1 to 3 m,
By setting R _{MD / TD} and R _{VD / TD} in the range of 0.3 to 3, it is possible to obtain a foam having a high strength and a beautiful appearance that could not be obtained in the past.

Claims (2)

[Claims] 1. A kneading agent is added to a modified polypropylene resin composition obtained by the reaction of a polypropylene resin, an aromatic vinyl monomer and a radical polymerization initiator,
Obtained by extruding the modified polypropylene resin composition in which a foaming agent is kneaded, the apparent density of the foam is 1
It is in the range of 0 to 300 kg / m ³ and has a thickness of 10 mm.
The above is the average diameter L _{TD of the} bubbles measured along the width direction of the foam, the average diameter L _{MD of the} bubbles measured along the extrusion direction of the foam, and the thickness direction of the foam. The measured average diameter L _VD of the bubbles is in the range of 0.1 to 3 mm, and the ratio of the average diameter L _MD of the bubbles to the average diameter L _TD of the bubbles is R _{MD / TD.} When the ratio of the average diameter L _VD of the bubbles to R _{VD / TD} is R _{VD / TD} , both R _{MD / TD} and R _{VD / TD} are composed of a modified polypropylene resin composition. Plate-shaped foam. 2. The closed cell ratio is 60% or more.
The plate-shaped foam described.